9 Things That Can Cause a Black Toenail and Treatments That Help

You might have dealt with a fungus that causes yellow toenails or white toenails, but discovering a black toenail can be a bit alarming. Unless you remember that you stubbed your toe recently, you’re probably wondering how you got it and what it means.

There are a few potential reasons for why your toenail is turning black or has black spots on it. Most don’t impact your overall health much, but some types of black toenails should definitely be checked out by your doctor as soon as possible.

Here are some reasons for a black toenail, how to treat it, and the ways you can prevent it.

Why you might have a black toenail

The most common cause for a black toenail is when the nail gets injured, trapping blood under the nail, explains Farah Moustafa, MD, FAAD, dermatologist and Director of Laser and Cosmetics at Tufts Medical Center. “It can look quite alarming, but closer evaluation with dermoscopy or light shows the purplish discoloration [is] trapped blood.” 

Still, a black toenail almost always requires some sort of treatment. While nail trauma is common, there are other, potentially more serious reasons your toenail can turn black, so it’s also important to know when to seek medical care. 

1. Blunt force trauma

Nothing elicits profanity as much as when a heavy object lands on your toe. It’s painful and, depending on the severity, can cause a black toenail. This occurs because blood can accumulate under the nail.

“Often this blood accumulates directly at the site of injury, which can be at the cuticle, in the middle of the nail, or closer to the tip,” says Joseph Zahn, MD, a dermatologist and assistant professor of dermatology at the George Washington University Medical Faculty Associates in Washington, D.C.

It can take several months for the black spot to move toward the tip and grow out with the nail.

In some cases, when intense toe pain and pressure from the nail bed are present, a doctor may need to drain the blood from under the nail. Never do this yourself. You could trigger an infection or cause more damage to the nail bed.

Eventually, the nail may look like it is coming loose from the nail bed. As tempting as it might be to pull it, let it fall off on its own, Dr. Zahn says. “The nail serves as the protector of the sensitive skin underneath, and it will be more comfortable to keep it until it falls off naturally.”

Treatment

Keep the toenail clean. If a piece of the toenail comes off creating a wound, apply antibiotic ointment and a bandage. Replace the bandage and reapply the antibiotic ointment daily until the wound closes up.

2. You’re wearing the wrong shoes

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Playing sports, running, or hiking hardly seems traumatic, but your toes beg to differ. This is especially true if you’re wearing improperly fitting shoes, causing your toes to constantly get pushed up against the cramped insides of the shoes.

“These individuals are also likely to have bleeding under the nail due to trauma and can result in thicker nails over time,” says dermatologist Shari Lipner, MD, PhD, an associate professor of clinical dermatology and Director of the Nail Division at Weill Cornell Medical Center.

The dried blood under the skin causes black toenails.

Treatment

Follow the same treatment plan for blunt force trauma. Wear cushioning pads if the toe hurts.

3. Toenail fungus (onychomycosis)

Otherwise known as toenail fungus, onychomycosis can cause brownish-black discoloration on the nails.

Distal subungual onychomycosis, a subtype, is a very common toenail fungus and the type most likely to cause brownish-black streaks in the center of the toenail. The fungus can invade underneath any toenail, but it tends to target the big toe the most.

As the fungus grows, there may be some mild discomfort and inflammation, and the toenail typically grows thicker, gets chipped or jagged, and lifts from the nail bed.

Treatment

With prescription antifungal medications applied daily for several months, the symptoms usually clear up, and the streaks grow out as the toenail grows.

4. A rare but serious form of skin cancer (acral melanoma)

If you spot a blackish-brown vertical streak or a triangle of brown-black pigment that goes along the entire length of the nail, call your doctor immediately.

Dr. Zahn says these are the hallmark signs of acral melanoma, a severe and aggressive form of skin cancer found on the soles of feet, palms of the hand, and under fingernails or toenails. Although rare, acral melanoma is the most common type of melanoma among people with darker skin.

If undetected, the black pigment can grow larger and wider. As the tumor progresses, it can become itchy, painful, and spontaneously bleed. Catching and diagnosing this melanoma is tricky, but timing is critical.

“As they are caught late, they have the opportunity to spread or metastasize other places and become more difficult to treat, or require more extensive surgery to remove them from the nail,” explains Dr. Zahn.

Treatment

The exact treatment varies depending on the biopsy results. A biopsy will determine how thick the melanoma is under the skin and how much needs to be removed.

“For all melanomas, the melanoma and a rim of healthy tissue surrounding the melanoma are removed to ensure all of the melanoma is taken out,” says Dr. Zahn.

5. An infection (paronychia)

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You may have never heard of it before, but paronychia is actually one of the most common infections in the United States. “[It’s] actually an infection and inflammation of the skin around the nail, not the nail itself,” Dr. Moustafa explains. 

It’s far more common on the hands than the feet, particularly if you regularly have your hands immersed in water, bite your nails, pull off hangnails, or pick at your cuticles. “This allows for bacteria to get in and cause inflammation and pain around the nail.” But it can happen on toenails too—especially if the skin around the toenail gets pierced by an ingrown toenail or injury.

The nails become painfully tender and swollen with red skin around the toenail and yellow pus under the cuticles.

Treatment

Paronychia is typically treated with topical and/or oral antibiotics, Dr. Moustafa says. If pus has built up in the skin around the nail, your doctor may make a small cut to drain the area to ease discomfort and encourage healing.

You can also manage paronychia symptoms at home, per 2023 research published in StatPearls. Soaking your feet in warm water for 10 to 15 minutes a few times a day (and then drying thoroughly) can help reduce pain and swelling—and in mild cases, the infection may go away on its own. But if you’re not seeing improvement (or developing more severe symptoms, like an abscess), make sure to see your doctor for treatment. 

6. Acute paronychia

Acute paronychia comes on suddenly from a trauma that pierces the skin, like an ingrown toenail or after pulling off that irritating hanging toenail that keeps snagging on the blanket. (Remember: Always use nail scissors or nail clippers.) “It is typically caused by bacteria, and is a result of a break of the skin around this area,” Dr. Moustafa says. This bacterial invasion leads to pain, redness, and swelling around the nail fold—either along the cuticle or the sides of the nail. 

Staphyloccocus (staph) bacteria is the primary culprit of the infection, causing pain and tender skin. “However, some paronychia is caused by a specific bacteria called Pseudomonas, which can cause a greenish or black discoloration of the nail,” says Dr. Moustafa.

Treatment

If an abscess is present, the infection requires drainage, per the StatPearls research. Warm foot soaks after this procedure encourage healing by allowing for continued drainage and keeping the infection from growing or spreading. 

Often, drainage followed by regular warm-water foot soaks may be enough, the research says. But if the pain, redness, and swelling aren’t improving or there are signs of a secondary infection (like cellulitis), your doctor will prescribe oral or topical antibiotics, which usually clear up the infection in a few days. 

7. Chronic paronychia

“Chronic paronychia is inflammation around the nail lasting for six weeks or more,” Dr. Moustafa explains. “It can affect any nails—both fingernails and toenails.”

There are many causes of chronic paronychia, she says, “including microorganisms such as bacteria or fungus, but it can also be caused by chemical irritation or allergic reactions.” 

That’s why chronic paronychia is more common in people who regularly have their hands in water containing irritants, chemicals, or detergents. But it can affect the toes, too, if your feet are regularly exposed to chemicals, such as those in cleaning products. The toenails can become brittle and rigid, and a portion of the toenail can turn a greenish-black color.

People who are exposed to long periods of wet or moist environments are also at risk, Dr. Moustafa says, like if you’re regularly walking around locker rooms or pool areas in bare feet.

Another risk factor: frequent, repetitive trauma to the nails—such as poorly-done pedicures and cuticle trimming or removal. “Rarely, some medications can cause chronic paronychia as well.” 

Treatment

Over-the-counter antibiotics can cause allergic reactions, so dermatologists rarely suggest them, Dr. Driscoll says. However, oral and topical prescription antifungal medicines are frequently necessary. 

“If the patient has paronychia at the site of the ingrown nail, then dermatologists may prescribe an oral antibiotic, possibly along with mupirocin, an antibiotic ointment that works well against Staphylococcal infections,” says dermatologist Marcia Driscoll, MD, associate professor of dermatology, University of Maryland School of Medicine in Baltimore.

It’s essential to keep the toes as clean and dry as possible while fighting chronic paronychia.

8. Washboard nails

David Petrus Ibars/Getty Images

Washboard nails look like, well, dirty washboards, with grooves that are dark brown to blackish. The habitual picking or pushing back of the cuticles causes injury under the nail each time you do it.

Over time, the blood trapped under the toenail from the trauma makes blackish grooves on the toenail. “With chronic picking, melanocytes (pigment-producing cells) in the nail matrix (nail growth center) activate to make pigment,” explains Dr. Lipner. The pigment gets mixed in and creates washboard-like grooves.

Washboard nails are associated with the compulsive disorder called onychotillomania.

Treatment

If you stop picking, the blood will grow out with the nail. If you don’t stop picking the cuticles, the discoloration can be permanent.

Breaking the habit is doable, but you might need help from a mental health professional.

9. Underlying health conditions

Nail discoloration can be a symptom of several chronic conditions, including diabetes, heart disease, kidney disease, gastrointestinal conditions, lung disease, and autoimmune diseases, according to 2024 research published in Clinical Dermatology Review. 

This nail discoloration doesn’t always present as a black toenail—and sometimes, these systemic diseases can affect the nails in other ways, too. But any issues involving the nails usually resolve once the underlying health condition is treated. 

Treatment

If you have unexplained changes to your nail color, shape, or texture, it’s recommended to check in with your doctor to screen for possible underlying health conditions. (Our nails reveal more about our health than you might think!) 

Tips to avoid getting black toenails

You can’t prevent some of the things that cause black toenails, like accidents that cause injuries to your toes. But you can follow these tips for healthy toenails.

1. Practice good nail hygiene

• Routinely check your toes and feet after bathing. You’ll spot trouble and be able to treat concerns faster.
• Don’t wear nail polish longer than a week or two. You can’t spot changes in your toenail if they’re covered in polish all the time.
• Trim your toenails straight across with slightly rounded corners. Sharp corners invite toenails to grow into the sides of the skin and cause sore ingrown toenails.

2. Take a warm foot bath and moisturize

• Soften thicker toenails that are difficult to cut. Place your feet in a warm bath using about a teaspoon of salt per pint of water. Let them soak for about 10 minutes. Dry thoroughly.
• Moisturize your toenails to make them easier to cut.
• Don’t forget the skin surrounding the nails. Dry and cracking skin is vulnerable to bacteria and fungus.

3. Wear comfortable footwear

• Wear properly fitted shoes. If you play sports, get a professional fitting.
• Wear shoes and socks that breathe and wick sweat and moisture away from your feet.
• Don’t walk barefoot in locker changing rooms, public showers, and pool decks.
• Put sunscreen on your toes when your feet are exposed to the sun.

When to see a doctor

In general, if there are signs of infection, such as redness, pus, pain, or swelling, it’s best to see your doctor ASAP before a black toenail becomes a bigger problem. This is particularly important if you have diabetes or circulation problems.

“As there are several causes for black toenails—including trauma, bacterial or fungal infections and rarely, melanoma—it is a good idea to be evaluated by a board-certified dermatologist who can take a closer look and help distinguish between these different causes, as the treatment will vary,” Dr. Moustafa explains. 

“This is especially important if you do not remember a clear trauma that would have caused the black toenail, as it might be one of these other causes that warrant further evaluation and treatment,” she says. 

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